I've actually admired this forum for a while and followed the odd thread but never registered until now. I probably know some of the members here who also frequent DIYelectriccar.com (where I am an admin).
Yeah, I found that trailer tail too although I didn't realize it was designed to collapse like that. Neat idea.
I'm not sure how easy this would be to do, but one thing I thought of on one of many drives in the rain (it rains a lot here......) was to try and either videotape or photograph a vehicle while it drives in light rain and use the image as a reference for where the drag comes from. The water mist tends to highlight any vortex as well as the airstream as it passes over the vehicle. Its also easy to see the big trailing wake behind the vehicle along with the typical stalled bubble in the pickup bed that mythbusters made famous a few years back (my 24~25 MPG runs were all with the gate up
). Although I suspect many here already knew that effect was real.
With a chase vehicle in the next lane and a good quality camera, it might be possible to use this as a reference for what works or what doesn't when trying different aeromods. Never tried this myself though, just thinking aloud. The other way is to simply tape small strings at several places all over the vehicle which wind tunnels still use to this day AFAIK.